Effect of low nitrogen content on work hardening and microstructural evolution in Hadfield steel

Nitrogen content in austenitic manganese steels is usually not reported nor standardized. The present work has found that it typically ranges between 130 ppm and 200 ppm in solution. Microstructural evolution has been studied by optical microscopy, using mainly differential interference contrast mode. Work hardening was analyzed under compression conditions using Hollomon's fitting and Vickers microindentation hardness measurements at different deformation levels. Even low contents of nitrogen in solution exhibit a significant effect on the slope of stress–strain curves, with strain-hardening exponent values of 0.7, 0.57 and 0.41 for 720 ppm, 130 ppm and 71 ppm of nitrogen, respectively. It was also found that the nitrogen content influences the microstructure of deformed coarse grained polycrystalline austenite, leading to twining and shear bands at the upper level of nitrogen, while it was not clearly found in the samples with lower nitrogen content.     

Square cup deep drawing and 2D-draw bending analysis of Hadfield steel

Hadfield steel is the dominant material in the production of bullet proof steel helmet for military uses. The conventional bullet proof steel helmets are extensively fabricated by cold forming (deep drawing) 1.2 mm Hadfield steel sheets at room temperature. This paper presents the experimental analysis of the square cup deep drawing and 2D-draw bending of Hadfield steel as a continuation of an international bench mark research program organized by NUMISHEET'93 organising committee in Japan. The draw-in values of the flange have been determined for various punch travels in the square cup operation. The principal strains were evaluated in three directions from grid measurments for those punch travels. Springback values and sidewall curls were also described in 2D-draw bending operation. The experimental results were compared with that of ones in mild steel.     

铬对高锰钢微观结构的影响

通过对含铬５％的国钢进行Ｘ射线衍射分析,发现奥氏体基体的衍射出现了（１１０）、（２１０）、（２１１）等晶面的超结构反射谱线,表明铬促进了高锰钢中合金元素的有序化倾向,同时为高猛钢加工硬化的动态应变时效（ＤＳＡ）机制和Ｍｎ－Ｃ对簇聚模型提供了实验依据。此外,ＴＥＭ观察到细小的颗粒碳化物,对其衍花样的标定确认为Ｍ２３Ｃ６型碳化物,说明铬在高锰钢中的碳化物不一定只以（Ｆｅ、Ｍ）３Ｃ的形式出现。     

Spray Deposition and Metal Atomisation Conference – SDMA 2003

Abstract

This conference, which incorporated the 5th International Conference on Spray Forming, was once again (after the successful 2000 event) held at Bremen University, under the auspices of Professor Bauckhage's group at IWT (Institut fu¨r Werkstofftechnik), reports JOHN DUNKLEY.     

Hydrogen environment embrittlement of stable austenitic steels

Seven stable austenitic steels (stable with respect to γ → α′ transformation at room temperature) of different alloy compositions (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N, 0.6C–23Mn, 1.3C–12Mn, 1C–31Mn–9Al, 18Cr–19Mn–0.8N) were tensile tested in high-pressure hydrogen atmosphere to assess the role of austenite stability on hydrogen environment embrittlement (HEE). The influence of hydrogen on tensile ductility was small in steels that are believed to have a high initial portion of dislocation cross slip (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N), while the effects of hydrogen were significantly greater in steels with other primary deformation modes (planar slip in 18Cr–19Mn–0.8N and 1C–31Mn–9Al or mechanical twinning in 0.6C–23Mn and 1.3C–12Mn) despite comparable austenite stability at the given test conditions. It appears that initial deformation mode is one important parameter controlling susceptibility to HEE and that martensitic transformation is not a sufficient explanation for HEE of austenitic steels.     

Impact wear behaviors of Hadfield manganese steel

Impact wear behaviors of Hadfield manganese steel at different impact angles were investigated. The results of impact wear tests show that there exists a critical impact load for Hadfield steel. The wear rate suddenly turns down after some impact cycles when the impact load is greater than the critical load. The critical impact load is smaller than 8.2 J in this research because the nano-sized austenitic grains embedded in amorphous delay the crack propagation in subsurface. From high resolution transmission electron microscope (HRTEM) examination of subsurface microstructure, it is found that a large amount of nano-sized grains embedded in bulk amorphous matrix are fully developed and no martensitic transformation occurs during the impact wear process. The analytical results of worn surface morphology and debris indicate that the initiation of crack, propagation and spalling are restricted in the amorphous phase, resulting in the size distribution of debris in nano-sizes, which is the reason why the wear rate of Hadfield steel is greatly decreased at high impact load.     

Abrasive Wear Behavior of High Chromium Cast Iron and Hadfield Steel-- A Comparison

 Abstract： Wear properties of two different crushers used for grinding raw materials of cement industry are compared using pin-on-disk wear test. The wear test was carried out with different loads on a pin. Abrasive wear behavior of two alloys was evaluated by comparing mass loss, wear resistance, microhardness and friction coefficient. The microstructure of the specimens was detected using optical microscope. The results showed that abrasive wear of high chromium cast iron is lower than that of Hadfield steel. Due to the presence of M7C3 carbides on the high chromium cast iron matrix, impact crushers exhibited higher friction coefficient.     

Effect of surface nanocrystallization on abrasive wear properties in Hadfield steel

A nanocrystalline surface layer was synthesized on a Hadfield steel by shot peening treatment. The microstructure evolvement of the surface layer of the shot peening treated sample was characterized by optical microscopy, X-ray diffraction and high-resolution transmission electron microscopy. It has been shown that the grain sizes in surface layer were decreased to 11.1-17.4 nm after 60 min shot peening duration. Surface hardness was also increased greatly. Two- and three-body abrasive wear experiments were carried out for work hardening and original specimens, separately. The results showed that the wear resistance of the nanocrystallized Hadfield steel has distinctly been improved in case of soft particles used as two-body wear abrasives or light impact load applied for impact abrasive wear.